Human Anatomy: Respiratory System Overview

Respiratory System Overview

• The respiratory system performs three main functions: air conduction, air filtration, and gas exchange.
• It's also involved in speech production (larynx) and the sense of smell (olfactory mucosa).
• The system is divided into a conducting portion and a respiratory portion. The conducting portion warms, moistens, and filters air. The respiratory portion is where gas exchange takes place.

Conducting Portion

• Includes nasal cavity, nasopharynx, oropharynx, larynx, trachea, and bronchi.
• Its function is to condition air.
• The nasal cavity and trachea have C-shaped hyaline cartilage for support.

Respiratory Portion

• Includes respiratory bronchioles, alveolar ducts, and alveoli.
• The site of gas exchange (oxygen and carbon dioxide).
• Alveoli are surrounded by a network of capillaries bringing blood close to inhaled air.
• The surface area of all alveoli together is roughly the size of a tennis court.

Respiratory Mucosa

• The respiratory mucosa consists of respiratory epithelium, basement membrane, and lamina propria.
• Epithelium can be ciliated simple columnar epithelium (in most of respiratory tract) or stratified squamous epithelium (larynx/pharynx), or pseudostratified ciliated columnar epithelium (nasal cavity).
• Contains goblet cells (mucus production), ciliated cells (mucociliary clearance), brush cells (sensory), basal cells (stem cells), and Clara/club cells (secretory and detoxifying).

Alveoli Structure

• Alveolar epithelium is mainly type I cells (flat squamous) and type II cells (cuboidal, surfactant secretion).
• Type II cells help ensure alveoli stay open.
• Alveoli are surrounded by a very thin blood-air barrier (capillaries).
• The capillaries bring blood into close proximity with the inhaled air within the alveoli.

Clinical Correlates

• Bronchitis is inflammation of the main airways (bronchi).
• Acute bronchitis is temporary and often caused by viral infections.
• Chronic bronchitis is characterized by mucus hyper-secretion, damaged cilia, chronic inflammation, and potential squamous metaplasia, which can cause COPD.

Nasal Cavity

• Divided into three regions: nasal vestibule, respiratory, and olfactory.
• Nasal Vestibule: Dilated space inside the nostrils.
• Respiratory Region: Largest part (inferior 2/3), lined by respiratory mucosa.
• Olfactory Region: Located at the apex of each cavity, lined by olfactory mucosa.
• Respiratory mucosa contains ciliated, pseudostratified columnar epithelium with goblet cells, brush cells, basal cells.

Nasal Cavity: Olfactory Region

• Olfactory mucosa has ciliated pseudostratified columnar epithelium.
• Unique cells include olfactory receptor cells (bipolar neurons), basal cells (stem cells) supporting columnar cells (similar to neuroglia).
• Bowman's glands produce a serous secretion to trap and dissolve scent molecules. — Abundant nerve fibers are present in the underlying connective tissue.

Pharynx

• Divided into nasopharynx, oropharynx, and laryngopharynx.
• Epithelium is non-keratinized stratified squamous epithelium to prevent drying.
• Supported by connective tissue with elastic fibers.

Larynx

• The passageway for air between the oropharynx and trachea.
• Contains vocal folds (vocal cords) lined with non-keratinized stratified squamous epithelium.
• Contains vocalis muscle (underlying skeletal muscle).

Trachea

• A short flexible tube part of the conducting airways.
• Its wall is composed of mucosa, submucosa, cartilaginous layer, and adventitia.
• Mucosa: Ciliated pseudostratified columnar epithelium with elastic fibers.
• Submucosa: Areolar connective tissue.
• Cartilaginous layer: C-shaped hyaline cartilage.
• Adventitia: Connective tissue, binding the trachea to surrounding structures.
• Trachea also contains small granule cells, and basal cells.

Bronchi

• The trachea bifurcates into two primary bronchi.
• The primary bronchi divide into segmental bronchi.
• A keel-shaped cartilage called carina is located within the tracheal bifurcation.
• The wall of the bronchi is composed of mucosa, muscularis, submucosa, cartilage layer, and adventitia.

Bronchioles

• Narrowest airways of the lung (0.5 mm)
• Deliver air to alveoli.
• Lack cartilage and glands.
• Simple ciliated cuboidal epithelium.
• Clara cells replace goblet cells.

Respiratory Bronchioles

• Involved in air conduction and gas exchange.
• Lined with simple cuboidal epithelium.
• Give rise to alveolar ducts.

Alveoli

• Sites of gas exchange between air and blood.
• Each alveolus is surrounded by capillary networks bringing blood into close proximity with inhaled air.
• Alveolar ducts are elongated airways.
• Alveolar sacs are clusters of alveoli.

Pulmonary Circulation

• The pathway of blood through the heart and lungs for oxygenation.
• Involves the pulmonary artery, pulmonary vein, and chambers of the heart.
• The lungs receive deoxygenated blood from the right side of the heart and return oxygenated blood to the left side of the heart.

Explore the key functions and components of the respiratory system in this quiz. Learn about air conduction, filtration, gas exchange, and the division into conducting and respiratory portions. Test your knowledge of structures like the nasal cavity, bronchi, and alveoli.